1. Field of the Invention
The present invention relates to a thin film magnetic head, a magnetic recording apparatus using the same and a method for manufacturing the same, and particularly to improvement of a thin film magnetic head.
2. Discussion of Background
In a write element provided inside a thin film magnetic head, a first pole portion and a second pole portion faces each other with a gap film between them at an air bearing surface (hereinafter, referred to as ABS) side (hereinafter, referred to as the front part), and a back gap is formed by joining a lower magnetic film connected to the first pole portion and an upper magnetic film connected to the second pole portion at the rear part opposite to the ABS. Around the back gap, a flat coil surrounding the back gap is positioned on a plane which is in parallel with the surfaces of the lower magnetic film and the upper magnetic film and nearly perpendicular to the ABS. The coil is formed generally by a frame plating method.
In a thin film magnetic head of this type, it is known that the shorter the yoke length YL from a back gap to a pole portion is, the more excellent high-frequency characteristic is obtained. In order to shorten the yoke length, it is necessary to reduce the number of turns of a coil positioned between the back gap and the pole portion or to decrease the width of the coil without reducing the number of turns.
However, since the number of turns of a coil is determined by a magneto motive force required, reducing the number of coil turns to shorten the yoke length YL has a limit.
On the other hand, in case of reducing the width of a coil without decreasing the number of turns, the electric resistance of the coil increases, so a temperature rise due to heat generation increases during a write operation. When the temperature rise increases, the first and second pole portions thermally expand to cause a thermal protrusion that the pole portions swell on the ABS. When a thermal protrusion occurs, the part where the thermal protrusion has occurred comes into contact with a magnetic recording medium and causes a head crash or causes damage or destruction of a magnetic record on the magnetic recording medium, so a thermal protrusion must be strictly avoided. If it is impossible to avoid a thermal protrusion, the floating height of a thin film magnetic head must be increased after all, which makes it impossible to meet a demand for a low floating height for a high recording density.
As a prior art which might be effective for solving the above-mentioned problem, there is U.S. Pat. No. 4,416,056. This prior art discloses a technique of patterning to form first conductors of the first layer arranged at fixed spaces on a plane, and then patterning to form second conductors of the first layer so that they fill up said spaces, insulated from said first conductors by an insulating film.
However, since this prior art discloses a structure in which the upper surfaces of the first conductors are covered with an insulating film, the sectional areas of the first conductors decrease by presence of the insulating film. In short, the above-mentioned prior art does not disclose a technique of maximizing the sectional areas of the first conductors.
And the above-mentioned prior art fails to disclose the relation of conductors relative to a pole portion and a back gap. Although the increase in wiring density of conductors contributes to shortening a yoke length YL, if the space between a conductor and each of a pole portion and a back gap is not made narrow, shortening the yoke length YL has a limit clearly.
Further, it is not necessarily preferable that the space between a conductor and each of a pole portion and a back gap is simply made narrow. The reason is that when the space between a conductor and each of a pole portion and a back gap is made narrow, there is a risk that the space which has not completely been filled up may make a keyhole.
As another prior art, there is U.S. Pat. No. 6,226,860B1. This prior art fails to disclose a means of solving the above-mentioned problem as well.